Low friction, self-acting gas bearings rely on the relative rotation of the bearing members to form the supporting bearing film from the ambient atmosphere. This atmosphere is usually air, but may be other gases if the bearing is sufficiently isolated. The gap or clearance between the surface of the rotating member and that of the stationary member is frequently on the order of one hundred microinches. Gas borne particles larger than this size can be sucked or drawn into the dynamically changing film and damage one or both of the mating bearing surfaces.
In some gas bearings, the gas required for the supporting film is supplied directly to the bearing from a pressurized source and is known as jacking fluid. Gas entering the source can be selected or filtered to prevent the entrance of oversized particles. Self-acting gas bearings, however, are usually started, stopped, and operate in an environment that includes the bearing drive or load or is amidst wear particles that are produced by nearby mechanisms. It then becomes difficult to insure that replenishment gas for the bearing film is clear of occasional oversize particles that can spall or gouge the bearing surface.
Attempts have been made to trap the damaging bits with filters in self-acting gas bearings, but the filters have been placed either at the entrance to the mechanism chamber enclosing the bearing, drive and load, which are themselves particle generators, or have been placed at the exit for the gas from the bearing. Typical of such arrangements are U.S. Pat. Nos. 4,656,545, issued Apr. 7, 1987 to K. Kakuta and 4,547,081, issued Oct. 15, 1985 to K. Tanaka et al. In each of these references, the gas for the supporting bearing film is either filtered as it enters a chamber enclosing a motor and disc drive or after the gas has passed through a drive motor and the gas bearing. The bearing gas is filtered too late to intercept wear or dirt particles and prevent them entering the narrow gas film opening crucial to bearing operation.